This application claims priority from Japanese Patent Application No. 00-192665, filed on Jun. 22, 2000, and Japanese Patent Application No. 00-357615, filed on Nov. 20, 2000, which are both incorporated by reference for all purposes.
This invention relates to shapes of holes of a flat electrode of electronic gun of cathode-ray tube for use in a display device, particularly in a CRT display device, and a method for processing the flat electrode, wherein three electron beam passage holes are formed in the flat electrode of electronic gun for improving the hole diameter precision and enhancing the resolution of focus lenses.
In recent years, the enhancement of the resolution of electronic gun components of a cathode-ray tube for color television has been increasingly demanded as the progress of the minuteness and definition of the image of color display. The resolution of an electronic gun can be enhanced by deterring the occurrence of bur which induces electron discharge as viewed from the improvement of the assembly precision of the electronic gun by highly precise components and the enhancement of the withstand voltage characteristics of the electronic gun.
A cathode-ray tube (FIG. 1) for color image display consists of a panel section 1 which is an image screen, a neck section 2 for accommodating the electronic gun, and a funnel section 3 which connects panel section 1 and neck section 2, and the funnel section 3 having a deflector which makes the electron beam 5 (Bc, Bs) emitted from an electronic gun 4 scanning on a fluorescent surface 6 of the color display.
Electronic gun 4 to be installed in the neck section 2 has various electrodes, such as a cathode electrode, control electrode, focusing electrode, and accelerating electrode. Electron beam 5 which is emitted from the cathode electrode is modulated by the signal to be applied to the control electrode. Modulated electron beam 5 is given a required sectional shape and energy through the focusing and accelerating electrodes. The formed and energized modulated electron beam is made to collide with fluorescent surface screen 6. On the way that the electron beam from electronic gun 45 reaches fluorescent surface screen 6, the electron beams are deflected to both the horizontal and vertical directions by the deflector installed in funnel 3 to form an image on fluorescent surface screen 6.
On the other hand, electronic gun 4 of this kind of color cathode-ray tube has a cylindrical electrode having a nearly elliptical peripheral shape, inside which flat electrodes having electron beam passage holes are disposed. (Japanese App. No. 59-215640).
FIG. 2 is a plan view showing a block diagram of such a flat electrode, and FIG. 3 shows a sectional view of the electron beam passage hole. The flat electrode has three electron beam passage holes 8, 9, and 10.
In the prior art, in the production of a flat electrode having the electron beam passage holes 8, 9, and 10, a flat electrode including electron beam passage holes was shaped by means of through punching using a usual press machine. In this case, as an enlarged sectional view of electron beam passage hole 9 of FIG. 3 shows, a sheared surface 11 and a broken-out surface 12 are formed on the inner surface of electron beam passage hole 9, resulting in a bur 13 on the outer surface of the metal plate. In the usual punching off method, sheared section length t1 accounted for about 60% of plate thickness t, while broken-out section length t2 accounted for as much as 40% of the plate thickness t. Further, some metal plates developed burs as high as 0.01 mm on their outer surfaces.
The existence of this broken-out section 12 causes distortion mainly in the focus lens. Accordingly, in a flat electrode of which a distortion developed in the focus lens is required to be as a particularly small as possible, such a method for punching out holes in the flat electrode is applied that when punching the flat electrode from the other side surface thereof, a hole smaller than the hole to be finally punched out is punched once, and after that a shaving method is applied to enlarge the hole until it finally meets a required diameter (Japanese App. No. 3-17964).
This shaving method, as the conceptual diagram of FIG. 4 shows, is required to punch metal plate 14 a few times to achieve a hole having a diameter D so that necessary electron beam can pass through. For example, a punch 15 that can make holes with diameters of 0.5D, 0.7D, 0.9D, and 1D in a metal plate is used to enlarge the hole diameter one by one until an objective length has been reached. As a consequence, the number of times required for punching increases. The use of such a punching process, in comparison with the usual punching off method, can reduce the thickness of broken-out surface to a range of 10-20% of plate thickness t and the length of bur 13 to below 0.005 mm. In order to achieve the high resolution of an up-to-date cathode-ray tube, more precise punching is required.
Further, bur 13 causes a decline of mainly the withstand voltage characteristic of the focus lens. Although an attempt is made to remove bur 13 from the outer edge of the hole by means of barrel grinding, the end of the hole may be rounded, and an excessive rounding at the end of the hole may result in undesirable distortion of the focus lens, thereby declining the resolution of the focus lens.
The purpose of the present invention is to provide a punching method for making the broken-out section 12 shorter compared with the conventional processing method to achieve flat electrode 7 without bur 13 and a desirable flat electrode of electronic gun.
In the color cathode-ray tubes of the prior art, a shaving method was used that requires punching a few times to punch out electron beam passage holes highly precisely on a flat electrode of electronic gun so that the number of times required for punching increases, resulting in a production cost increase. In addition, because even this shaving method leaves problems that the broken-out section length of around 20% and the difficulty of removing bur completely, there was a limitation in the enhancement of the withstand voltage characteristic of electron beam.
It is an object of the present invention to provide a method for resolving the problems, and in order to achieve the above-mentioned object, a cathode-ray tube has a metal plate having a hole, wherein electron beam passes through, and wherein the hole is different in diameter between the upper surface and lower surface of the metal plate.
Further, in order to achieve the aforementioned object, a cathode-ray tube of a metal plate having a hole, through which an electron beam from the electrode of an electronic gun passes through; wherein there exists a difference in the diameter of the hole between the upper and lower surfaces of the metal plate; and wherein the pertinent difference in diameter is within a range of ratio from 0.01 to 0.4 relative to the metal plate.
Further, in order to achieve the aforementioned objects, a cathode-ray tube of a metal plate, through which an electron beam from the electrode of an electronic gun passes; wherein there exists a difference in the diameter of the hole between the upper and lower surface of the metal plate; and wherein the pertinent difference in diameter is within a range of ratio of 0.01-0.2 relative to the metal plate.
Further, in order to achieve the aforementioned objects, a cathode-ray tube of a metal plate, through which an electron beam from the electrode of an electronic gun passes; wherein there exists a difference in the diameter of the hole between the upper and lower surfaces of the metal plate; wherein there exists a difference in the diameter of the hole, wherein there exists a difference in the hole pitch between the upper and lower surfaces of the metal plate; and wherein the ratio of the difference in the hole pitch on the upper surface thereof to that on the lower surface thereof is in a range from 0.95 to 1.05.
Further, in order to achieve the aforementioned object, cathode-ray tube has a metal plate having holes through which electron beams from the electrode of an electronic gun pass, wherein the shapes of holes on the exit sides of electron beams are elliptic, with the existence of a difference in diameter of said holes between the upper and lower surfaces of said metal plate and with the existence of a difference in hole pitch between the upper and lower surface of said plate.
Further, in order to achieve the aforementioned objects, in a flat electrode of electronic gun for the cathode-ray tube, the elliptic ratio (the ratio of the major axis to the minor axis of ellipse) of the shape of electron beam passage hole on the exit side of electron beam is within a range from 1.002 to 1.08.
Further, in order to achieve the aforementioned objects, the flat electrode of electronic gun is characterized in that, in a metal plate having holes through which electron beam passes, the holes have more than one diameters in the thickness direction of the metal plate.
Further, in order to achieve the aforementioned objects, the flat electrode of electronic gun is characterized in that, in the shape of holes through which electron beams from the electrode of electric gun pass, the diameters of the holes on one surface of the metal plate are greater than that on the other surface thereof.
Further, in order to achieve the aforementioned objects, a metal plate electrode for electronic gun is characterized in that, the difference in the diameter of a hole of the metal plate electrode, through which an electron beam from the metal plate electrode passes, between the hole diameter on one surface side of the metal plate electrode and the other surface side thereof is within a range of 1-40%.
Further, in order to achieve the aforementioned objects, a metal plate electrode for an electronic gun is characterized in that, in the shape of a hole through which an electron beam from the metal electrode for the electronic gun passes, the hole diameter is formed to flare out to form a trumpetlike shape in such a direction from the inside of the greater hole diameter to the surface of the metal plate.
Further, in order to achieve the aforementioned objects, a production method is characterized by such a production method for punching a hole in a metal plate using a punch and a die, where punching is started from the surface on one side of the metal plate and stopped in a middle section of the plate thickness, followed by punching the hole continuously until a middle section of the plate thickness from the other surface side.
Further, in order to achieve the aforementioned object, a production method for punching a metal plate is characterized by such a production method for punching the metal plate using a punch and a die where the punch for use in the punching process, which is started from one surface side and is stopped in a middle section of the plate thickness of the metal plate, has a diameter greater by 1 to 40% of the thickness of the metal plate than the diameter of the die.
Further, in order to achieve the aforementioned objects, a production method for punching a metal plate is characterized in that a punch for use in the punching process which is stopped in a middle section of the thickness of the metal plate has an elliptic sectional shape.
Another object of the present invention is to provide the processes of punching a metal plate using a punch and die with a method to stop punching in a middle section of the thickness of the metal plate on one surface side of the metal plate at the first processing stage, and a method to punch an electron beam passage hole from the other side at the second processing stage, thereby providing the electronic gun with a hole shape superior in withstand voltage characteristic. Further, in order to achieve the aforementioned objects, in the punching process stages for punching an electrode part of an electronic gun, it is desirable for the diameter of a hole punched at the first processing stage to be greater than the diameter of the hole punched at the second processing stage. Preferably, it is desirable for the diameter of the hole punched at the first processing stage to be greater by 1 to 40% of the thickness of the metal plate than the die diameter to achieve smooth finishing of the sheared inner surface of the hole.
Further, in order to achieve the aforementioned objects, in the process of punching an electrode part for an electronic gun, it is desirable to stop punching in a middle section of the first processing stage when the punching comes to a position ranging of 50-90% of the thickness of the metal plate to achieve smooth finishing of the inner surface of the hole.
Further, in order to achieve the aforementioned objects, in the process of punching an electrode part for an electronic gun, when it is required to punch a plurality of holes (e.g., three holes) in an electrode part on which the interval between adjacent holes is narrower than the hole diameter as shown in FIG. 3, it is desirable to punch the holes into an elliptic sectional shape to form the hole diameter on the punch side to be completely round.
Furthermore, in order to achieve the aforementioned objects, in the process stages of punching a plurality of holes, when punching is stopped in the middle of the first processing stage, it is desirable to half-off punch or cut the whole or part of the peripheral section of an electrode part for an electronic gun to form the hole diameter on the punch side to be substantially round.